50 TUE WASATCH AXl; iiUlDGEK FAUNiE. 



ingly from tlie typical Tnjgones in the form of the caudal spines. These 

 are trigonal in section, ami l)ear a ventral keel, and a serrate edge on 

 each side. The extinct species of the Monte Bolca Eocene, Trygon muricata, 

 has, according to Gazzola, the spine of the true Trygones. 



XlPHOTRYGON ACUTIDENS CopC. 



American Naturalist, May, 1879 (April). 



Plato I, figs. 1-5. 



This species is of graceful proportions, having no great transverse 

 expansion, and possessing a long and slender tail. The size is inferior to 

 that of a fully-grown skate, but much exceeds that of the Cyclohatis oligo- 

 dactylus of the Lebanon. 



The ossification of the superficial part of the cranial cartilage is wide, 

 extending to the branchial fissures below. It terminates anteriorly, in a 

 sliglitly concave truncation, a short distance in front of the orbital open- 

 ings. Two convex lobes immediately behind the mouth, divided by a 

 median fissure, resemble the labial flaps. They are marked by rather 

 larger hexagons than the other surface. The least hexagons form a longi- 

 tudinal oval patch on the middle line behind these flaps, which corresponds 

 in position to the superior fontanelle. Posterior to the scapular arch the 

 ossification forms a band on each side of the vertebral column, and, gradu- 

 ally narrowing, disappears near the origin of the caudal spines. 



The proptervgia extend well forward, giving outline to an acute snout. 

 They are segmented to the extremity. The outline of the fin expands 

 gradually from this apex. The metapterygial border is very stout, and is 

 not so long as the propterygial. The posterior border of the pectoral fin 

 does not extend quite so far posteriorly as the posterior border of the ven- 

 tral fin. The latter, in turn, extends for about three-fourths the length of 

 the claspers from the base of the fin. Pectoral rays; metapterygial, 31; 

 mcsopterygial, 10; propterygiiil, 41. 



The vertebra^ are fully ossified; the caudal series becomes very slender 

 distally, and measures nearly twice as long as from the pehac arch to the 

 anterior border of the cephalic ossification. In the specimen described 

 there are three caudal spines situated near together, whose origins are a 



